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Two masses m1=5 kg and m2=9 kg are connected by a string which passes over

  1. Feb 12, 2012 #1
    1. The problem statement, all variables and given/known data

    two masses m1=5 kg and m2=9 kg are connected by a string which passes over a massless frictionless pulley. the masses are moving with an acceleration a as shown. the coefficient of kinetic friction between m1 and surface of the table is 0.1 calculate the acceleration of block 1, the acceleration of block 2 and the tension in the string.

    http://t0.gstatic.com/images?q=tbn:...phsGvO7lUMigQiON8sOud2-zoII78Enu2kNXFs1XNGIdg

    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Feb 12, 2012 #2

    ojs

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    You don't show any attempt at a solution, are you completely lost?

    What is your first intuition? What forces are at work here? What is the main principal that we should use regarding forces?
     
  4. Feb 12, 2012 #3

    ojs

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    You don't show any attempt at a solution, are you completely lost?

    What is your first intuition? What forces are at work here? What is the main principal that we should use regarding forces?
     
  5. Feb 12, 2012 #4
    i answered the first box like that but im not sure
    a= (Fa - Fr)/m
    a= 49-4.9/(5) = 8.82
    because it is in the X axis so no angle.

    in the second part i don't know what i should do
     
  6. Feb 12, 2012 #5

    ojs

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    Almost the right way to find the acceleration but you are calculating the forces incorrectly.

    Ok, here is what you have to do, consider all the forces at play here, there is the gravity force pulling on both the masses but only one of the gravity forces causes the masses to move, the gravity force on mass 1 is the same as the normal force on mass 1 which leads to a friction force that deters the acceleration. So you need to find the total force on the system (by subtracting the friction force from the gravitation force that is causing the movement) and that will be equal the total mass (not only the 5kg) times the acceleration that you are searching for.
     
  7. Feb 12, 2012 #6

    ojs

    User Avatar

    Almost the right way to find the acceleration but you are calculating the forces incorrectly.

    Ok, here is what you have to do, consider all the forces at play here, there is the gravity force pulling on both the masses but only one of the gravity forces causes the masses to move, the gravity force on mass 1 is the same as the normal force on mass 1 which leads to a friction force that deters the acceleration. So you need to find the total force on the system (by subtracting the friction force from the gravitation force that is causing the movement) and that will be equal the total mass (not only the 5kg) times the acceleration that you are searching for.
     
  8. Feb 12, 2012 #7
    Could u plz tell me the final answer ?
     
  9. Feb 13, 2012 #8

    ojs

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    Unfortunately for you thats not how we do things around here.
     
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